According to AFP, including the world’s top polluters China and the United States, signed the Paris climate deal Friday, boosting hopes of quick action on combating global warming.

French President Francois Hollande was the first leader to put his signature to the accord during a ceremony at the United Nations, followed by leaders from island-states hardest hit by climate change.

Held on Earth Day, the ceremony comes four months after the hard-won deal was clinched in Paris and marks a first step toward binding countries to the promises they made to cut greenhouse gas emissions.

“This is a moment in history,” UN Secretary-General Ban Ki-moon told leaders gathered at the UN General Assembly.

“Today you are signing a new covenant with the future.”

Holdout countries still have a year to sign the deal, but the focus has now turned to swift ratification and entry into force before the target date of 2020.